The water content of coal tars is one of its more variable and troublesome characteristics. Associated with this water content are ammonium compounds, in particular ammonium chloride, to which much of the equipment corrosion during tar distillation can be attributed. While the addition of alkali to the tar will reduce the corrosion, the usually non-volatile alkali compound remains in the pitch residue following distillation, often affecting its properties adversely.
Attempts have been made, with varying degrees of success to eliminate or diminish the water content of the tar. The less successful ones have included addition of electrolyte, modification of the tar pH, freezing of the tar, and subjecting the tar to high frequency mechanical agitation. Among the more successful processes has been boiling the tar. Nonetheless such a procedure is rather energy intensive and generally fails to achieve an adequate reduction in the water content of the tar.
Another problem that has plagued the users of tar is the often high (and also variable) content of quinoline insolubles (Q.I.) therein. The problem is particularly noticeable when these insolubles are concentrated in the pitch residue following the distillation of the tar. The particulate nature of Q.I. renders difficult virtually any process which requires the passage of the pitch through small orifices, e.g. in the impregnation of porous, baked carbon bodies. Additionally, should the Q.I. have a high inorganic portion, the combustion rate of the carbon body produced by coking (or otherwise carbonizing) the pitch will be significantly increased. It is believed that the water and Q.I. are associated with each other to form the disperse phase of a stable emulsion in the coal tar material which is difficult to break by conventional means.
The stability of such emulsions has presented a hitherto intractable problem to the person attempting a separation. An earlier attempt (described in "Use of Surface Active Agents For Improving Separation of Tar-Water Emulsions" - Tadeusz Patzek - Koks, Smola, Gaz 1968, 13 (11), (330), at such a separation describes the results as follows: "In the case of coal tar-water emulsions that sep. well on standing, all chemicals accelerated the phase sepn, and improved the dewatering of the tar. In the case of stable emulsions, however, none of the prepns. was effective in sepg. the phases even when the emulsions were heated and allowed to stand for up to 120 hrs. There was no sepn. on the tar phase contained 20-30 % or more H.sub.2 O. In some cases, it appeared that the surfactant added as an emulsifier, causing added stabilization of the emulsions." (from Chemical Abstracts, Vol. 70 (1969) no. 108114Z).
Another problem often encountered during the handling or transport of coal-tar material is the adhesion and/or deposition of coal-tar components on surfaces contacting the coal-tar material.
Accordingly, it is an object of this invention to provide an improved process for the dewatering of tars.
It is also another object of this invention to decrease the quinoline insoluble content in the tar.
It is yet another object of the present invention to provide a means whereby the afore mentioned adhesion and tar deposition of coal-tar material components on contacting surfaces is minimized.